The present invention relates to fifth wheel assemblies generally utilized for tractor-trailer combinations. More specifically, the present invention relates to a fifth-wheel bearing plate with a reduced weight structure providing equivalent bearing plate surface areas to prior similar fifth wheel bearing-plate surfaces from the present applicant for contact with trailer wear plates. However, the bearing plate is shorter in overall length, includes a more ovate shape, wider kingpin receiving slot, a more continuous upper surface, has thinner support ribs and fillets to improve casting practice and lower production costs as well as the weight of the bearing plate.
Fifth wheel assemblies on tractors broadly encompass a bearing plate, a coupling mechanism with trailer kingpin guide means, mounting brackets for mating the assembly with the tractor, a jaw-release handle and a locking jaw. The locking jaw is opened to receive and retain a mating kingpin extending from a trailer with a wear plate. After mating of the kingpin and fifth wheel jaw, the jaw mechanism locks to secure the kingpin, and thus the trailer, to the fifth wheel. The trailer wear plate bears against the bearing plate planar surface, which contacting surfaces suffer wear during turning or pivoting. In addition, the fifth wheel jaw must be adjusted, as in present practice, for the kingpin or there will be a resultant slack in the jaw.
Fifth wheel assemblies are predominantly utilized on commercial or revenue-generating tractors, although notice is taken of their usage on a limited number of recreational trailer applications. The fifth wheel structures are broadly divided by their weight carrying capacity. As over-the-road tractors generally are susceptible to state imposed weight limitations in their carrying capacity, there is an ongoing effort in the industry to reduce the tractor gross vehicle weight and thus to increase the payload capacity of the tractor-trailer arrangements or increase fuel economy.
Reduction in fifth-wheel weight cannot preclude safety and load bearing considerations, which are related to the fifth-wheel physical parameters. The particular style, shape or construction of the fifth wheel may be dependent upon the manufacturer. However, the fifth-wheel performance characteristics and apparatus will include the ability to couple with a kingpin, the strength to bear typical highway service loads, which include longitudinal (both buff and draft) loads, vertical loads, transverse loads and overturning (roll) loads, a locking jaw capable of retaining the kingpin and trailer coupled, and a jaw unlocking mechanism for disengagement of the kingpin and trailer.
Efforts have been made to reduce the weight of the fifth wheel, especially on flatbed railcars for piggyback transport, by casting the fifth wheel plate of aluminum for lightweight construction. However, the cast aluminum fifth wheels did not have sufficient physical strength to withstand the stresses normally encountered by fifth wheels. Thus, fifth wheel hitches continue to be primarily manufactured of cast steel or formed structural steel. As noted in U.S. Pat. No. 4,659,101 to Buckley, the weight of the fifth-wheels is not only a drawback on collapsible railroad flatbed stanchions but the fifth wheel weight is a considerable addition to the weight of a conventional truck tractor. This Buckley--'101 patent teaches a forged aluminum bearing plate and depending abutments for the locking jaws. A forged aluminum fifth wheel provides the strength necessary to withstand the normal tractor-trailer service stresses. However, it is known that forged fifth-wheel products are considerably more expensive to produce than are cast fifth-wheel products. This fifth-wheel hitch taught in the Buckley--'101 patent may also be manufactured by steel casting or steel fabrication. Although the focus of this Buckley--'101 patent is primarily directed to the locking jaw mechanism, the disclosure also discusses the concept of mass reduction and the benefits therefrom for a fifth wheel assembly.
U.S. Pat. No. 4,221,397 to Holt teaches a trailer hitch head with jaws to bear all kingpin wear. However, the illustrated top or bearing plate is shown with a generally rectangular configuration demonstrating that bearing plate shape is not limited to an oval, elliptical or circular shape. One of the problems to be overcome with any of the disclosed fifth-wheel structures is excessive top plate wear and avoidance of this wear reduces repair, renovation or replacement of the top plate and trailer wear plate prior to their expected life cycle. The Holt--'397 disclosure alludes to flatcar service, but the teaching of the fifth wheel structure is not limited to such flatcar service.
A second aluminum fifth wheel structure is shown in U.S. Pat. No. 4,208,062 to Maassen, and this fifth-wheel structure is fabricated to be a high-strength, low-weight assembly. However, it is implied in the description that the top bearing plate and the bottom plate are cast aluminum with vertical frames, which top and bottom plates are subsequently bolted together to reduce the total mass of the assembly. The total weight of a given assembly or a percentage reduction in weight is not noted in the disclosure.
Other illustrations of fifth wheel shapes, locking mechanisms and mounting apparatus are shown in the following U.S. Pat. Nos.: 2,621,056; 2,640,707; 2,648,544; 4,946,183; 4,477,100; 4,333,666; 3,813,114; 3,578,357; 3,013,815; 3,640,549; 2,861,818; and 2,581,254. All of these patented apparatus are cast or formed steel and iron components, which iron-based structures have an inherent weight problem related to the physical weight to strength relationship of the material. That is, the density of the iron is relativiely large, thus, manufacture of a component with a fixed surface area and thickness requisite for a specified strength characteristic results in a heavy structure. The mass of a fifth-wheel necessary to carry both the static vertical load and the trailing load adds to the gross vehicle weight and consequently reduces the payload carrying capacity or the fuel economy of the tractor-trailer combination. Therefore, it is an ongoing effort to reduce the mass of the fifth wheel while maintaining its strength and load-bearing capacity.